1. Field of the Invention
The invention generally relates to uncoated particles of reversed cubic phase or reversed hexagonal phase material containing an active. In particular, the invention provides uncoated particles having an ionic charge that is sufficient to stabilize the particles in dispersion in a liquid, e.g. a polar solvent.
2. Background of the Invention
Many active compounds used in pharmaceutical, nutritional, nutriceutical, environmental, and industrial uses are either insoluble in water, or perform better when delivered in some sort of protective, targetable, and/or otherwise functional matrix. In the case of pharmaceuticals, it is generally recognized that microparticles can provide robust matrices for drugs by various routes of administration, provided they are of appropriate size, stable in dispersion, and composed of excipients that are acceptable for that route. However, in addition to solubilizing and/or protecting the active compound for administration and/or in circulation, it would be advantageous for a microparticle to play an active role in the delivery and absorption of the active, a goal that has been a stumbling block for a number of potentially useful particulate and droplet-based vehicles.
For the case of pharmaceutical actives that are of low solubility in water, solubilization of such drug compounds is made challenging by the very limited selection of solvents and structured liquids that are approved by regulatory bodies for use at levels that would be required to solubilize the drug. Furthermore, water-miscible liquid excipients, most notably ethanol, are of limited value since, even when the drug is soluble in neat ethanol, for example, it will often precipitate upon contact with water, such as with either diluent water for injection or in the aqueous milieu of body fluids, such as blood.
Nanostructured lyotropic liquid crystalline phases of the reversed type—namely reversed cubic and reversed hexagonal phases—have been developed as excellent solubilizing matrices for both poorly-soluble compounds, and for such delicate compounds as proteins and other biomacromolecules. U.S. Pat. No. 6,482,517 (Anderson, Nov. 19, 2002) and U.S. Pat. No. 6,638,621 (Anderson, Oct. 28, 2003), the contents of which are incorporated in their entireties by reference, disclose, among other things, effective compositions and methods for producing such lyotropic liquid crystalline matrices. These particles are coated with solid materials.
A pioneer in surfactant phase behavior, P. A. Winsor, described particles of cubic phase coated with a nanostructured liquid phase, which in accordance with current knowledge was probably an L3 phase. See Liquid Crystals & Plastic Crystals, Vol. 1, eds. G. W. Gray and P. A. Winsor (1974), Ellis Horwood Ltd., page 224, as well as Balinov, Olsson and Soderman (1991) J. Phys. Chem. 95:5931. Larsson, in 1989, described reversed cubic phase particles with lamellar liquid crystalline phase coatings. See Larsson (1989) J. Phys. Chem. 93(21) 7304.
U.S. Pat. No. 5,531,925 (Landh et al., Jul. 2, 1996) likewise describes particles of reversed cubic or reversed hexagonal phase which require a surface phase of either lamellar liquid crystalline, lamellar crystalline, or L3 phase, in order to disperse the particles. The coating is referred to in that disclosure as a “surface phase”, or “dispersible phase”, thereby teaching, first, that it is a distinct, separate phase from the reversed liquid crystalline interior, and second, that the reversed liquid crystalline phase interior is itself not a dispersible phase. The L3 surface phase in that disclosure is described as being “anchored to the bi- or mono-layer of the interior phase” (column 7, lines 59-60).
U.S. Pat. No. 6,071,524 describes compositions in the form of dispersions containing: (a) 60 to 98% by weight of an aqueous phase and (b) 2 to 40% by weight of an oily phase dispersed in the aqueous phase, the oily phase being dispersed and stabilized by using cubic gel particles. The particles are essentially formed of 0.1 to 15% by weight (relative to the total weight of the composition) of at least one unsaturated fatty acid monoglyceride having a C16-C22 unsaturated fatty chain in a mixture with phytanetriol, and 0.05 to 3% by weight relative to the total weight of the composition of a dispersing and stabilizing agent. The agent is a surface active substance, water-soluble at room temperature, containing a linear or branched, saturated or unsaturated, fatty chain having 8 to 22 carbon atoms. The patent also describes methods of making such compositions. A minimum of three thermodynamically distinct phases are present in such a mixture, namely the aqueous exterior phase, the cubic gel particles, and the oil phase containing the active. The active substance (drug, cosmeceutical compound, etc.) is present in the dispersed oily phase, and in fact substantially localized in the oily phase. Such systems, emulsions in which lipid or surfactant monolayers, multilayers, lamellar or non-lamellar liquid crystalline domains or lamellar crystalline domains stabilize droplets of one fluid in another, suffer from poor suitability for targeting, shelf-life limitations (creaming, breaking of emulsions, etc.), and other problems well known in the art of emulsions. And emulsions or droplet systems in which each droplet is surrounded by a plurality of particles of another material or phase, all undergoing independent diffusion around the droplet (and, by definition, are separated from one another by intervening fluid layers), suffer from gaps between the particles that compromise the ability of the material to control the egress of active out of, or ingress of confounding factors into, the droplet. Furthermore, with such a system wherein the plurality of particles surrounding the droplet are derived from lyotropic liquid crystals, as in U.S. Pat. No. 6,071,524, in the body of an animal these particles can readily become independent of the droplets, such that the droplets, which contain the vast majority of the active, do not reap the potential benefits (as discussed herein) of the liquid crystalline particles. Although the “cubic gel particles” of U.S. Pat. No. 6,071,524 are designed to aggregate at the surface of the oil droplets, in a pharmaceutical application the high dilution factors and shear forces, together with the myriad of biochemical conditions and processes encountered by a droplet, could readily strip the droplets of their intended coating. Another limitation of the invention described in U.S. Pat. No. 6,071,524 is that neither the monoglycerides nor the phytanetriol (nor many of the other surfactants used in the reported embodiments) is approved for use in injectable pharmaceutical products, and indeed monoglycerides are known to be extremely toxic upon injection.
U.S. application 2002/0153509 (Lynch et al, published Oct. 24, 2002) describes compositions in which charged compounds are used as “anchors” (“tethers”), serving to anchor active compounds or targeting compounds to cubic phases, sometimes in particulate form. For example, it is stated in the disclosure of 2002/0153509 that the inclusion of an anchor such as a cationic surfactant could increase the amount of active drug in the cubic phase in proportion to the amount of surfactant (e.g., paragraph 0099), in accordance with the schematic picture shown in FIG. 2 of that disclosure which depicts an anionic ketoprofen molecule associated with the head group of a cationic surfactant (and situated on the polar side of the polar-apolar interface). The anchor's purpose is to bind a drug molecule, on a 1-to-1 molecule basis.
It would be desirable to have improved microparticles for drug solubilization and protection that are of an appropriate size, stable in dispersion, and composed of excipients that are acceptable for administration via a variety of routes. In addition, it would be desirable to have improved microparticles that also play an active role in the delivery and absorption of the drug.